Examples of known thermoplastic polymers having two or more polymer segments which are radially extended from a central segment of the polymers are as follows: a hybrid star-shaped polymer having a condensed polymer segment and acrylic addition polymer segments which are radially extended from the condensed polymer segment (Japanese Official Patent Provisional Publication (Kokai) No. Showa 63-132914); a star-shaped polymer having a structure including a diphenylethylene derivative at its center from which three polymer segments formed by polymerization are radially extended (Japanese Official Patent Provisional Publication (Kokai) No. Heisei 3-190911); a star-shaped polymer having a structure in which a polyfunctional crosslinking agent having at least two polymerizable double bonds is included at the polymer center from which two or more polymer segments formed by polymerization are radially extended (Japanese Patent Publication (Kohyo) No. Heisei 5-500827); a star-shaped block polymer formed by photo-initiated radical polymerization utilizing a dithiocarbamate group (Poly. J., vol. 16, p. 511 (published 1984)); a star-shaped block polymer formed by thermal-cleavage radical polymerization utilizing a triphenylmethyl group that is introduced into a terminal of a polymer (Poly. Bull., vol. 16, p. 277 (published 1985)); and so on.
In the above-mentioned conventional star-shaped polymers, the centers of the radial structures derive from the condensed polymer, diphenylethylene derivative, the polyfunctional crosslinking agent, the polyfunctional polymerization-initiator, and the like. Therefore, the combination of the polymer segments is limited, the polymer segments are limited to those which derive from homopolymers, the type of monomer units constituting the polymer segments is limited, or the irradiation of light (ultraviolet rays) is needed and the permeability of monomers in a depth direction is too weak for industrial mass production. Thus, the conventional star-shaped polymers are only utilized in very limited industrial fields and expensive.
In addition, in the above-mentioned conventional star-shaped polymers, blocks of an identical polymer cause phase separation, whereby the transparency is deteriorated and the mechanical strength is weakened.